Supercharged internal combustion engine

ABSTRACT

A turbocharged internal combustion engine with exhaust return via a valve on the intake side of the turbocompressor unit to the engine intake side. The turbine and the compressor of the turbocompressor unit are adapted to each other and to the engine in such a way that the pressure on the inlet side of the turbine is always higher than the pressure on the pressure side of the compressor. The rotary shaft of the unit is coupled via a drive chain containing a continuously variable transmission to the crank shaft of the engine. An electronic control unit controls the transmission ratio and the degree of opening of the valve.

BACKGROUND OF THE INVENTION

The present invention relates to a supercharged internal combustionengine comprising firstly a turbocompressor unit with an exhaust driventurbo unit, which has an inlet communicating with the exhaust side ofthe engine, and a compressor unit, which has a suction sidecommunicating with the surrounding atmosphere and a pressure sidecommunicating with the engine intake side, and secondly an exhaustrecirculation valve coupled between the exhaust side of the engine andthe inlet of the turbo unit, said valve being settable for recirculationof a certain portion of the exhaust to the engine intake side.

DESCRIPTION OF THE RELATED ART

Exhaust can be returned to the intake side of a supercharged engine inessentially two different ways, each having different advantages anddisadvantages, namely before or after the compressor. The simplestmethod technically would be to connect the recirculation line to thesuction side of the compressor, but in that case the exhaust must passthrough the compressor and then through the charge air cooler which isusually present. A significant disadvantage of this is however, that allthe components would in time become coated with harmful soot from theexhaust. This disadvantage can be avoided by introducing the exhaustdownstream of said components but if a turbo unit is used with thedesired high efficiency, the charge air pressure will be higher than theexhaust pressure within the normal operating rpm range of the engine,which means that some form of pump device is desired which increases theexhaust pressure to a level above the charge air pressure. Asupercharged engine with an exhaust pump in the form of an ejector pumpis known by SE-A-9301093-2.

SUMMARY OF THE INVENTION

The purpose of the present invention is in general to achieve asupercharged internal combustion engine of the type described by way ofintroduction which permits return of exhaust to the intake sidedownstream of the compressor without requiring an exhaust pump. This isachieved according to the invention by virtue of the fact that the turbounit and the compressor unit are so adapted to each other and to theengine that, within the normal operating speed range of the engine, theexhaust pressure on the inlet side of the turbo unit is higher than thecharge air pressure on the pressure side of the compressor unit.

As regards design, this can be achieved with a turbocompressor which isdimensioned so that the pressure fall over the turbine will be greaterthan normal. A certain loss of efficiency in the turbo unit is in thiscase unavoidable.

In a preferred further development of the engine according to theinvention, the turbo unit is coupled to the engine crank shaft via areduction gearing and a continuously variable transmission. The losswhich arises when redistributing the pressures can thus be recovered sothat final result will be a net gain despite the increase in the exhaustpressure on the intake side of the turbo unit. An engine with thesecharacteristic features thus fulfills three important conditions. Bycombining the setting of the degree of opening of the valve towards theengine intake side with a suitable setting of the rpm of the compressorwith the aid of the continuously variable transmission, both the exhaustpercent and the amount of air on the intake side can be freelycontrolled at each point on the operational curve of the engine at thesame time as the compound arrangement permits exhaust return without anyloss of efficiency.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described in more detail below with reference toexamples shown in the accompanying drawing where the FIGURE showsschematically one embodiment of an engine installation with a sixcylinder internal combustion engine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The engine 1 in the FIGURE can be a four stroke diesel engine. It showsa turbocompressor unit, generally designated 2, which comprises a turbounit 3 and a compressor unit 4. The turbo unit 3 is connected on itssuction side 5 to an exhaust conduit 6 including an adjustable three wayexhaust return valve 7, to which an exhaust conduit 8 is also connected.The conduit 8 is connected via an exhaust cooler 9 to the engine intakemanifold (not shown). The outlet 10 from the turbo unit is connected toan exhaust pipe 11. The compressor 4 is connected on its inlet side 12via a conduit 13 to an intake filter (not shown) and on its outlet side14 via a conduit 15 to a charge air cooler 16 to the engine intakemanifold. As can be seen from the FIGURE the conduit 8 is connected tothe engine charge air side downstream of the charge air cooler 16 which,in addition to avoiding soot deposit in the cooler, is advantageous asregards function due to the fact that there is a pressure drop over thecooler.

The turbocompressor unit 2 has a rotary shaft 17, which is coupled, viaa high speed gearing 18, a continuously variable transmission (CVT) 19and a low speed gearing 20, to the engine crank shaft 21. In thecomponent chain from the rotary shaft 17 to the crank shaft 21 there canbe included a clutch and/or torsion damper, by means of which thedriving connection between the rotary shaft 17 and the crank shaft 21can be broken. In the high speed gearing IS a first rpm reduction isprovided from the operating rpm of the turbo unit of approximately100,000 rpm down to the CVT operating rpm of about 10,000 rpm. In thelow speed gearing 20, the rpm is reduced further to the operating rpm ofthe crank shaft of about 2,000 rpm.

The transmission ratio in the CVT 19 and the degree of opening of thevalve 7 towards the conduit 8 is controlled by an electronic controlunit 22, which contains a microprocessor, in which the amount ofreturned exhaust and the amount of air is programmed for eachoperational point within the normal operational speed range of theengine, which can be expressed simply as being the rpm range frommaximum engine torque to maximum engine power. The turbo unit 3 and thecompressor unit 4 are furthermore dimensioned relative to each other andto the engine so that the pressure in the exhaust conduit 6 is alwayshigher than the pressure in the charge air conduit 15 within the normalengine operating range. The smaller the pressure difference is, the morethe valve 7 must be open towards the conduit 8 to provide a given amountof exhaust. The amount of air is controlled by the compressor rpm, whichis regulated by the CVT. The control unit 22, which controls this, canbe the electronic control unit which is present in most modem enginesand which controls all engine functions as a function of vehicle enginedata fed into the control unit from sensors known per se and not shownin more detail here.

The invention has been described above with reference to a preferredembodiment which has a transmission with a continuously variabletransmission ratio, i.e. of the type which is usually called CVT. Withinthe scope of the invention there can be also be used fixed geartransmissions in which the transmission ratio can be varied in steps, orhydraulic transmissions, electrical transmissions or other types oftransmissions with variable transmission ratios.

We claim:
 1. Supercharged internal combustion engine, comprising:aturbocompressor unit with an exhaust driven turbo unit, said turbo unithaving an inlet communicating with the exhaust side of the engine, and acompressor unit, said compressor unit having a suction sidecommunicating with the surrounding atmosphere and a pressure sidecommunicating with the engine intake side; an exhaust recirculationvalve coupled between the exhaust side of the engine and the inlet ofthe turbo unit, said exhaust recirculation valve being settable forrecirculation of a certain portion of the exhaust to the engine intakeside; a transmission, with a variable transmission ratio, coupling theturbo unit to an engine crank shaft, the turbo unit and the compressorbeing coupled via a rotary shaft, the turbo unit being coupled to thecrankshaft of the engine; and a control unit for controlling thetransmission ratio to limit an energy transfer direction from the turbounit gas to the crankshaft wherein, within the normal operating speedrange of the engine, the exhaust pressure on the inlet side of the turbounit is higher than the charge air pressure on the pressure side of thecompressor unit.
 2. Internal combustion engine according to claim 1,wherein the turbo unit is coupled to the crank shaft of the engine via areduction gearing.
 3. Internal combustion engine according to claim 1,wherein the transmission has a continuously variable transmission ratio.4. Internal combustion engine according to claim 1, wherein thecompressor unit communicates with the intake side of the engine via acharge air cooler and that the valve communicates with the engine intakeside downstream of the charge air cooler.
 5. Internal combustion engineaccording to claim 1, wherein the valve communicates with the engineintake side via an exhaust gas cooler.
 6. Internal combustion engineaccording to claim 2, wherein the valve and the transmission withvariable transmission ratio are controlled relative to each other by anelectronic control unit.